Method and apparatus for allocating resource of multiple carriers in ofdma system

ABSTRACT

Provided is a Physical Downlink Control Channel (PDCCH) transmission method of a base station for a mobile communication system based on an Orthogonal Frequency Division Multiple Access (OFDMA). The method includes acquiring downlink control information of a resource corresponding to a carrier among a plurality of carriers, identifying at least one Control Channel Element (CCE) index based on an indicator of the carrier among the plurality of carriers, generating a PDCCH for the downlink control information based on the identified CCE index, and transmitting the PDCCH through a predetermined carrier.

PRIORITY

This application is a Continuation of U.S. application Ser. No.13/056,864, which was filed in the U.S. Patent and Trademark Office onJan. 31, 2011, as a U.S. National Stage of International ApplicationPCT/KR2009/004263, filed Jul. 30, 2009, and claims priority to KoreanPatent Application No. 10-2008-0074918, which was filed in the KoreanPatent Office on Jul. 31, 2008, the content of each of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resource allocation method andapparatus for an Orthogonal Frequency Division Multiple Access (OFDMA)system and, in particular, to a resource allocation method and apparatusfor an OFDMA-based mobile communication system that allows allocatingresources of multiple carriers.

2. Description of the Related Art

Recently, Orthogonal Frequency Division Multiplexing (OFDM) is becomingvery popular for modern broadband wireless communication systems and the3rd Generation Long Term Evolution (3GPP LTE) has adopted OFDM. LTEdefines a Physical Downlink Control Channel (PDCCH), which conveysUE-specific control information including downlink resource allocation,uplink resource allocation, and broadcast control channel LTE Advanced(LTE-A) is a major enhancement of 3GPP LTE to meet target data rates of1 Gbits for high mobility and 100 Mbits low mobility with very highspectrum allocation of 100 MHz by aggregating multiple 20 MHz LTE bands.With the increase of system bandwidth, it is plotted to evolve to 5LTE-A systems while maintaining use of 20 MHz LTE bands.

The downlink resource allocations of the conventional LTE and LTE-A aredescribed with reference to FIGS. 1 and 2.

An LTE-A system can be implemented by aggregating 4 LTE systems usingthe LTE bands. Referring to FIG. 1, in the LTE system using the firstfrequency band f 1, a sub-frame is composed of 14 OFDM symbols of whichup to three can be used for control channels. In FIG. 1, three OFDMsymbols are used for the control channels exemplarily. Here, a PhysicalDownlink Control Channel (PDCCH) can be encoded at different codingrates (CRs) depending on the channel condition and transmitted on 1, 2,4, or 8 Control Channel Elements (CCEs), where a CCE corresponds to 9Resource Element Groups (REGs) and an REG corresponds to 4 OFDMsubcarriers. FIG. 1 shows an exemplary case in which the PDCCH istransmitted on two CCEs for allocating downlink resource. A base stationinforms a user equipment of the downlink resource with the resourceallocation information within the PDCCH. In case of LTE-A system, thebase station allocates downlink resources to the UE for the respectivefrequency bands (i.e. f1, f2, f3, and f4) using individual PDCCHs. Forinstance, the PDCCH of f1 is used for allocating traffic channelresource for f1, and the PDCCH of f2 is used for allocating trafficchannel resource for f2. The LTE-A system depicted in FIG. 1 isimplemented for use of wider frequency band while reusing all thefunctionalities of LTE system. Here, the downlink resource allocation bytransmitting the PDCCH on two 2 CCEs is depicted as an example, but incan be applied for uplink resource allocation and resource allocationusing a MIMO function.

FIG. 2 shows an exemplary downlink resource allocation technique inwhich the downlink resources for the entire system frequency bandincluding f1, f2, f3, and f4 are allocated using a single PDCCH infrequency band f4. In the system of FIG. 2, a PDCCH of a frequency bandincludes additional information on the other bands for the UE todiscriminate the downlink resources allocated in different frequencybands.

Although it is advantageous to allocate the resources of frequency bandsof different LTE systems using a single frequency band, the conventionalresource allocation method has a drawback in that the information amountincreases due to the additional information for discriminating thefrequency bands.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to address at least theproblems and/or disadvantages described above and to provide at leastthe advantages described below.

An aspect of the present disclosure provides a Physical Downlink ControlChannel (PDCCH) transmission method of a base station for a mobilecommunication system based on an Orthogonal Frequency Division MultipleAccess (OFDMA), with the method including acquiring downlink controlinformation of a resource corresponding to a carrier among a pluralityof carriers, identifying at least one Control Channel Element (CCE)index based on an indicator of the carrier among the plurality ofcarriers, generating a PDCCH for the downlink control information basedon the identified CCE index, and transmitting the PDCCH through apredetermined carrier.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a downlink resource allocationprocedure of a conventional LTE system;

FIG. 2 is a diagram illustrating a downlink resource allocationprocedure of a conventional LTE-A system;

FIG. 3 is a diagram illustrating a concept of structuring downlinkcontrol channels for a resource allocation method according to thepresent invention;

FIG. 4 is a diagram illustrating an exemplary resource allocationprocedure according to the first embodiment of the present invention;

FIG. 5 is a diagram illustrating a concept of the resource allocationmethod according to the second embodiment of the present invention;

FIG. 6 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the secondembodiment of the present invention;

FIG. 7 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the thirdembodiment of the present invention;

FIG. 8 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the fourthembodiment of the present invention;

FIG. 9 is a block diagram illustrating a configuration of a base stationapparatus for transmitting multiple PDCCHs carrying multicarrierresource allocation information according to an exemplary embodiment ofthe present invention;

FIG. 10 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the first embodiment ofthe present invention;

FIG. 11 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the second embodiment ofthe present invention;

FIG. 12 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the third embodiment ofthe present invention;

FIG. 13 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the fourth embodiment ofthe present invention;

FIG. 14 is a block diagram illustrating a configuration of a userequipment for receiving multiple PDCCHs in different frequency bandaccording to an exemplary embodiment of the present invention;

FIG. 15 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the first embodiment ofthe present invention;

FIG. 16 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the second embodiment ofthe present invention;

FIG. 17 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the third embodiment ofthe present invention; and

FIG. 18 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the fourth embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention are described withreference to the accompanying drawings in detail. The same referencenumbers are used throughout the drawings to refer to the same or likeparts. Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention. The terms used in the following descriptionsare defined in consideration of the corresponding functions in thepresent invention and thus can be replaced with other words according tothe intention and practice of user and operator. Accordingly, thedefinitions of the terms should be made based on the contents throughthe entire description of the present invention.

Recently, various researches have been conducted for improving highspeed data transmission efficiency of mobile communication systems usingOrthogonal Frequency Division Multiplexing (OFDM) technologies. OFDM isa multicarrier modulation (MCM) scheme for transmitting data throughmultiple subcarriers in parallel. In an OFDM system, an input symbolstream is divided into several sub-symbol streams and modulated intomultiple orthogonal subcarriers for transmission.

The origins of OFDM started in the late 1950 s with the FrequencyDivision Multiplexing for military communication purposes, OFDM usingorthogonal overlapping multiple subcarriers has been developed in 1970 sbut limited in wide spread used due to the difficult of implementingorthogonal modulations between multiple carriers.

With the introduction of the idea of using a Discrete Fourier Transform(DFT) for implementation of the generation and reception of OFDMsignals, by Weinstein, in 1971, the OFDM technology has developedrapidly. Additionally, the introduction of a guard interval at the startof each symbol and use of cyclic prefix (CP) overcomes the negativeeffects caused by multipath signals and delay spread.

With such technical advances, the OFDM technology is applied in variousdigital communications fields such as Digital Audio Broadcasting (DAB),Digital Video Broadcasting (DVB), Wireless Local Area Network (WLAN),and Wireless Asynchronous Transfer Mode (WATM). That is, theimplementation of OFDM could be accomplished by reducing implementationcomplexity with the introduction of various digital signal processingtechnologies such as Fast Fourier Transform (FFT) and Inverse FastFourier Transform (IFFT). OFDM is similar to Frequency DivisionMultiplexing (FDM) but much more spectrally efficient for achieving highspeed data transmission by overlapping multiple subcarriersorthogonally. Due to the spectral efficiency and robustness to themultipath fading, OFDM has been considered as a prominent solution forbroadband data communication systems.

Other advantages of OFDM are to control the Intersymbol Interference(ISI) using the guard interval and reduce the complexity of equalizer inview of hardware as well as spectral efficiency and robustness to thefrequency selective fading and multipath fading. OFDM is also robust tothe impulse noise so as to be used for communication systems.

As aforementioned, the 3GPP LTE also has adopted OFDM as one of the keytechniques. In the LTE system, the Physical Downlink Control Channel(PDCCH) is used as a downlink control channel for downlink resourceallocation, uplink resource allocation, and uplink resource allocationbroadcast control channel transmission. In the meantime, the LTE-A isplotted to secure 100 MHz bandwidth by aggregating 20 MHz bandwidths of5 LTE systems and evolve to 5 LTE-A systems while maintaining use of 20MHz LTE bands.

FIG. 3 is a diagram illustrating a concept of structuring downlinkcontrol channels for a resource allocation method according to thepresent invention.

Referring to FIG. 3, the downlink control channel is mapped on theresource elements in up to 3 OFDM symbols in time domain and variablenumber of subcarriers in frequency domain. In frequency-time domain, theresource elements that are not used for Reference Signal (RS) aregrouped into Resource Element Blocks (REGs) each consisting of fourresource blocks, 9 REGs corresponds to a Control Channel Element, and aPDCCH is transmitted on 1, 2, 3, and 8 CCEs. In FIG. 3, each PDCCH istransmitted on two CCEs, i.e. PDCCH 0 on CCE 9 and CCE 10, PDCCH 1 onCCE 14 and CCE 15, PDCCH 2 on CCE 16 and CCE 17, and PDCCH 3 on CCE 19and CCE 20.

In an exemplary embodiment of the present invention, the first CCE amongthe CCEs assigned for the PDCCHs is used for CCE index information. Themethod and apparatus for allocating resources of multiple carriers in amobile communication according to the present invention is described inthree exemplary embodiments.

FIG. 4 is a diagram illustrating an exemplary resource allocationprocedure according to the first embodiment of the present invention.

In the first embodiment of the present invention, a plurality of PDCCHsallocated in different frequency bands for a user equipment are arrangedin order of the indices of CCEs on which the PDCCHs are transmitted. ThePDCCHs arranged in the CCE index order are used for allocating resourcesin different frequency bands, and the base station allocates the trafficresource within a frequency band using the PDCCHs as follows. In anexemplary embodiment of the present invention, the PDCCH can be used forthe purpose of uplink or downlink resource allocation or Multiple InputMultiple Output (MIMO) resource allocation. Multiple PDCCHs can begenerated with different types or different Downlink Control Indicators(DCIs). For instance, the PDCCH of the first frequency band f1 can carrya downlink grant for Single Input Single Output (SISO) while the PDCCHof the second frequency band f2 carries downlink grant for MIMO. Themultiple PDCCHs can be used for allocating multiple uplink resources ormultiple downlink resources or multiple uplink and downlink resources toa user equipment.

The resource allocation method according to the first embodiment of thepresent invention operates as follows. The base station scheduler firstacquires the information on the resources to be allocated within therespective frequency bands. Next, the base station scheduler determinesthe numbers of PDCCHs to be used in the respective frequency bands onthe basis of channel conditions of control channels of the respectivefrequency bands. Next, the base station transmits, when a frequency bandin which the number of PDCCH is 1 exists, the PDCCH on the controlchannel of the corresponding frequency band. In the resource griddenoted by reference number 40, transmitting the PDCCH in the frequencyband f3 means that the PDCCH is used for allocating resource within thefrequency band f3. Finally, the base station transmits multiple PDCCHsof different frequency bands, as arranged in index order of CCEs onwhich the PDCCHs are transmitted, through the control channel of onefrequency band.

As shown in the resource grid denoted by reference number 40, theresources of the frequency bands f 1, f2, and f4 are allocated using thecontrol channel of frequency band f4. In this case, the PDCCH determinedfor allocating the resource of the frequency band f1 is transmitted onthe CCEs having the lowest CCE indices, the PDCCH determined forallocating the resource of the frequency band f2 is transmitted on theCCEs having the next lowest CCE indices, and the PDCCH determined forallocating the resource of the frequency band f4 is transmitted on theCCEs having the highest CCE indices. That is, the base station arrangesthe multiple PDCCHs in ascending index order of CCEs on which the PDCCHsare transmitted and maps the CCE indices to the indices of the frequencybands f 1, f2 and f4 arranged in ascending order as shown in the partdenoted by reference number 45 of FIG. 4.

A method for locating the resources allocated within the respectivefrequency bands in a user equipment is described hereinafter. Referringto the resource block 40 of FIG. 4, the user equipment receives thePDCCH for the frequency band fi3 through the control channel of thefrequency band f3 and the PDCCHs for the frequency bands f 1, f2, and f4through the control channel of the frequency band f4.

The user equipment first locates the resource allocated within thefrequency band of which control channel is carrying a single PDCCH. Thefrequency band of which control channel is used for carrying the singlePDCCH is excluded when locating the resources using the multiple PDCCHstransmitted in one frequency band. Next, the user equipment receives themultiple PDCCHs through the control channel of the frequency band f4;locates the resource indicated by the PDCCH referenced with the lowestCCE index within the frequency band f1, the resource indicated by thePDCCH reference with the next lowest CCE index within the frequency bandf2, and resource indicated by the PDCCH reference with the highest CCEindex within the frequency band f4.

In the first embodiment of the present invention, the resources ofmultiple frequency bands are allocated using the order of indices of theCCEs on which the PDCCHs are transmitted. Here, a rule should beincluded that the aggregation of multiple PDCCHs can be allowed for onefrequency band. This means that the each of the rest frequency bands isallowed for carrying one or no PDCCH. This is because the mappingbetween the CCEs indices referencing the PDCCHs and frequency bandindices can become complex if multiple PDCCHs are transmitted inmultiple frequency bands.

FIG. 5 is a diagram illustrating a concept of the resource allocationmethod according to the second embodiment of the present invention.

Referring to FIG. 5, the resource allocation method according to thesecond embodiment of the present invention allocates resources ofmultiple frequency bands using the CCE index information of the multiplePDCCHs transmitted in one frequency band. As shown in FIG. 5, the numberof CCEs on which the PDCCH is transmitted is 1, 2, 4, or 8 and can bepresented in the form of a tree. That is, the PDCCH transmitted on asingle CCE is indicated with the CCE index (0, 1, 2, 3, . . . ), thePDCCH transmitted on two CCEs is indicated with the index of the firstone of two consecutive CCEs (0, 2, 4, 8, . . . ), the PDCCH transmittedon three CCEs is indicated with the index of the first one of fourconsecutive CCEs (0, 4, 8, 12), and the PDCCH transmitted on four CCEsis indicated with the index of the first one of 8 consecutive CCEs (0,8, 16, . . . ).

In the user equipment, the demodulation is performed with a commondemodulation region and a dedicated demodulation region in the controlchannel. In order to reduce power consumption of the user equipment, thebase station transmits the PDCCH in the common demodulation region andthe dedicated demodulation region, and the user equipment demodulatesthe data in the common and dedicated demodulation regions. In thisembodiment, the resources of multiple frequency bands are allocated inthe demodulation region dedicated to the user equipment. The informationon the frequency band in which the multiple PDCCHs are transmitted canbe expressed as equation (1).

(First CCE index of PDCCH/L_PDCCH)mod N_freq=freq.index  (1)

where L_PDCCH denotes a length of PDCCH, i.e. a number of CCEs on whichone PDCCH is transmitted. That is, when a PDCCH is transmitted on 4CCEs, L_PDCCH is 4. N_freq denotes a number of entire availablefrequency bands.

How to indicate frequency information using equation (1) is describedwith an exemplary case.

FIG. 6 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the secondembodiment of the present invention. In FIG. 6, reference number 60denotes a set of frequency bands in which multiple PDCCHs aretransmitted in some frequency bands (frequency bands f3 and f4) but noPDCCH in some frequency bands (frequency bands f1 and f2), and referencenumber 62 denotes a PDCCH-frequency band mapping scheme when the L_PDCCHis 1 and the N_freq is 4, reference number 64 denotes a PDCCH-frequencyband mapping scheme when the L_PDCCH is 2 and the N_freq is 4, andreference number 66 denotes a PDCCH-frequency band mapping scheme whenthe L_PDCCH is 4 and the N_freq is 4.

How the PDCCHs are mapped to the frequency bands are described withreference to the PDCCH-frequency band mapping scheme 64 in which theL_PDCCH is 2 and the N_freq is 4. In this case, the PDCCHs, arranged asshown in the set of frequency bands 60, can be referenced with the CCEindices of 0, 2, 4, 6, and 8, and theses CCE indices are interpretedinto PDCCH indices of 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3 using equation(1). Assuming that the PDCCH indices are designated as follows: index0=f4, index 1=f3, and index 2=f2, and index 3=f1.

In a second embodiment, the base station can allocate the resources ofmultiple frequency bands using the PDCCH indices referencing the PDCCHs.For instance, the resource of the frequency band f2 can be allocated bytransmitting the PDCCH of which PDCCH index is 1.

A resource allocation method using the rule of equation (1) according tothe third embodiment of the present invention is described hereinafter.FIG. 7 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the thirdembodiment of the present invention. In FIG. 7, reference number 70denotes a set of frequency bands in which multiple PDCCHs aretransmitted in some frequency bands (frequency bands f1 and f4) and onePDCCH in some frequency bands (frequency bands f2 and f3), and referencenumber 75 denotes a PDCCH-frequency band mapping scheme when the L_PDCCHis 2 and N_freq is 4.

In a third embodiment, when a single PDCCH is transmitted in a frequencyband, the resource of the corresponding frequency band is allocatedwithout abiding by the rule of equation (1). Otherwise, when multiplePDCCHs are transmitted in a frequency band, a specific frequency bandcan be indicated using the PDCCH abiding by the rule of equation (1). Inthe third embodiment, the resource of the frequency band in which aPDCCH is transmitted can be allocated with multiple PDCCHs that aretransmitted in another frequency band.

FIG. 8 is a diagram illustrating an exemplary resource allocationoperation in the resource allocation method according to the fourthembodiment of the present invention. In the fourth embodiment of thepresent invention, the resource of the frequency band in which a PDCCHis transmitted cannot be allocated with multiple PDCCHs that aretransmitted in another frequency band unlike in the third embodiment. InFIG. 8, reference number 80 denotes a set of frequency bands in whichmultiple PDCCHs are transmitted in some frequency bands (frequency bandsf1 and f4) and on PDCCH in some frequency bands (frequency bands f2 andf3), and reference number 85 denotes a PDCCH-frequency band mappingscheme in which the value of N_freq is reset to 2 by excluding thefrequency bands in which one PDCCH is transmitted.

In order for the user equipment to reduce the power consumption causedby decoding all CCEs which the user equipment searches for, the basestation transmits a 1-bit information, along with the PDCCH having thelowest PDCCH index, indicating whether the current frequency band isused for transmitting a single PDCCH or multiple PDCCHs.

FIG. 9 is a block diagram illustrating a configuration of a base stationapparatus for transmitting multiple PDCCHs carrying multicarrierresource allocation information according to an exemplary embodiment ofthe present invention.

As shown in FIG. 9, the base station apparatus includes a PDCCHgenerator 100, an f1 transmitter 110, an f2 transmitter 120, an f3transmitter 130, and an f4 transmitter 140.

The PDCCH 100 generates PDCCHs to be transmitted in respective frequencybands using system information. The transmitters 110 to 140 performsIFFT on the PDSCH DATA generated by Physical Downlink Shared Channel(PDSCH) generators (not shown) and the PDCCH data and transmits the IFFTtransformed data through corresponding frequency bands. In FIG. 9, fourtransmitters (i.e. f1 to f4 transmitters) 110 to 140 operating on thefrequency bands f1 to f4 are depicted as an example. Each of the f1 tof4 transmitters 110 to 140 can be provided with a plurality of PDCCHtransmitters 111-1 to 111-N, a PDSCH transmitter 118, a PDCCH selector112, an IFFT 113, an Cyclic Prefix (CP) handler 114, and an RFtransmitter 115.

The PDCCH transmission operation is described with the example of the f1transmitter 110. A plurality of PDCCH transmitters 111-1 to H 1-Nprocess the corresponding PDCCH data output by the PDCCH generator 100so as to output the PDCCH data in an appropriate transmission format,and the PDCCH selector 112 selects one or more PDCCH outputs of thePDCCH transmitters 111-1 to 111-N. The PDSCH transmitter 118 processesthe PDSCH data output by a PDSCH generator (not shown) so as to outputthe PDSCH data in an appropriate transmission format. The IFFT 113performs IFFT on the PDCCH data output by the PDCCH selector 112 and thePDSCH data output by the PDSCH transmitter 118, the CP handler 114 addsa CP to the IFFT transformed data, and the RF transmitter 115 transmitsthe output signal of the CP handler 114 after up-converting to the radiofrequency signal.

Here, the f2 to f4 transmitters 120 to 140 have the same internalconfiguration as the f1 transmitter f1. Accordingly, each of the f1 tof4 transmitters 110 to 140 performs IFFT on the PDCCH data output fromthe PDCCH selector 112 and the PDSCH data output from the PDSCHtransmitter 118 by means of the IFFT 113, adds a CP to the signal outputby the IFFT 113, and transmits the CP-inserted signal afterup-converting to a radio signal by means of the RF transmitter 115through a corresponding frequency band, i.e. one of f1 to f4.

FIG. 10 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the first embodiment ofthe present invention.

Referring to FIG. 10, the base station apparatus first determineswhether a number of PDCCHs to be transmitted in the current frequencyband is equal to or less than one (202). The number of PDCCHs can bezero, one, or more. If the number of PDCCHs to be transmitted in thecurrent frequency band is equal to or less than one, then the basestation apparatus at step 202 determines whether the number of PDCCH tobe transmitted is one (204). If the number of PDCCH to be transmitted isnot one, i.e. zero, then the base station apparatus terminates the PDCCHtransmission procedure.

Otherwise, if the number of PDCCH to be transmitted is one, then thebase station apparatus transmits the PDCCH by means of a correspondingfrequency band transmitter (206) and terminates the PDCCH transmissionprocedure. If the number of PDCCHs to be transmitted in the currentfrequency band is not equal to or less than one at step 202, i.e. ifmultiple PDCCHs are transmitted in the current frequency band, then thebase station apparatus arranges the multiple PDCCHs on the CCEs of thecurrent frequency band in consideration of the original frequency bandsof the PDCCHs such that the index of the first one of CCEs for carryingeach PDCCH can be interpreted into a frequency band index (208), andtransmits the arranged multiple PDCCHs by means of a correspondingfrequency band transmitter (210). That is, when multiple PDCCHs forallocating the resources of different frequency bands are required to betransmitted through a single frequency band, the base station apparatusarranges the multiple PDCCHs on the CCEs of the current frequency bandthat are interpreted into the indices of the original frequency bands ofthe PDCCHs, and transmits the PDCCHs arranged as such on the CCEs. Atthis time, the frequency bands in which one PDCCH is transmitted areexcluded from the list of the candidate frequency bands for transmittingmultiple PDCCHs.

FIG. 11 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the second embodiment ofthe present invention.

Referring to FIG. 11, the base station apparatus first determineswhether a number of PDCCHs to be transmitted in the current frequencyband is equal to or less than one (302). If the number of PDCCHs to betransmitted in the current frequency band is equal to or less than one,then the base station apparatus determines whether the number of PDCCHsis one (304). If the number of PDCCHs to be transmitted is not one, i.e.zero, then the base station apparatus terminates the PDCCH transmissionprocedure. Otherwise, if the number of PDCCHs to be transmitted is one,then the base station apparatus transmits the PDCCH which is referencedwith a CCE index in the current frequency band (306) and terminates thePDCCH transmission procedure. If the number of PDCCHs to be transmittedin the current frequency band is not equal to or less than one at step302, i.e. if multiple PDCCHs are required to be transmitted in thecurrent frequency band, then the base station apparatus arranges themultiple PDCCHs (including the PDCCHs for allocating the resources ofthe frequency band in which one PDCCH is transmitted already) on theCCEs of the current frequency band such that the corresponding CCEindices are interpreted into the frequency band indices by usingequation (1) (308), and transmits the multiple PDCCHs by means of thecorresponding frequency band transmitter (310). It is noted that theresource of the frequency band in which one PDCCH is transmitted can beallocated with another PDCCH transmitted in the current frequency bandagain at step 308.

In short, the PDCCH transmission procedure according to the secondembodiment of the present invention is performed as follows. When noPDCCH is required to be transmitted in the current frequency band, thePDCCH transmission procedure is terminated. When one PDCCH is requiredto be transmitted in the current frequency band, the PDCCH istransmitted on the CCEs that are randomly selected in the currentfrequency band. When multiple PDCCHs are required to be transmitted inthe current frequency band, the PDCCHs are transmitted on the CCEs ofwhich indices are interpreted into the frequency band indices by usingequation (1).

FIG. 12 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the third embodiment ofthe present invention.

Referring to FIG. 12, the base station apparatus first determineswhether a number of PDCCHs to be transmitted in the current frequencyband is equal to or less than one (402). If the number of PDCCHs to betransmitted in the current frequency band is equal to or less than one,then the base station apparatus determines whether the number of PDCCHsis on (404). If the number of PDCCHs to be transmitted is not one, i.e.zero, then the base station apparatus terminates the PDCCH transmissionprocedure. Otherwise, if the number of PDCCHs to be transmitted is one,then the base station apparatus transmits the PDCCH which is referencedwith a CCE index in the current frequency band (406) and terminates thePDCCH transmission procedure. If the number of PDCCHs to be transmittedin the current frequency band is not equal to or less than on at step402, i.e. if multiple PDCCHs are required to be transmitted in thecurrent frequency band, the base station apparatus arranges the multiplePDCCHs (excluding the PDCCH for allocating the resource of the frequencyband in which one PDCCH is transmitted already) on the CCEs of thecurrent frequency band such that the corresponding CCE indices areinterpreted into the frequency band indices by using equation (1) (408),and transmits the multiple PDCCHs by means of the correspondingfrequency band transmitter (410). It is noted that the resource of thefrequency band in which one PDCCH is transmitted cannot be allocatedwith another PDCCH transmitted in the current frequency band at step 408unlike the second embodiment.

In short, the PDCCH transmission procedure according to the thirdembodiment of the present invention is performed as follows. When noPDCCH is required to be transmitted in the current frequency band, thePDCCH transmission procedure is terminated. When one PDCCH is requiredto be transmitted in the current frequency band, the PDCCH istransmitted on the CCEs that are randomly selected in the currentfrequency band. When multiple PDCCHs are required to be transmitted inthe current frequency band, the PDCCHs are transmitted on the CCEs ofwhich indices are interpreted into the frequency band indices by usingequation (1).

FIG. 13 is a flowchart illustrating a resource allocation method for anOFDMA-based communication system according to the fourth embodiment ofthe present invention.

Referring to FIG. 13, the base station apparatus first determineswhether there is at least one PDCCH to be transmitted in the currentfrequency band (502). If no PDCCH to be transmitted exists, the basestation apparatus terminates the PDCCH transmission procedure.Otherwise, if there is at least one PDCCH to be transmitted in thecurrent frequency band, the base station apparatus arranges the at leastone PDCCH on the CCEs of the current frequency band such that thecorresponding CCE indices are interpreted into the frequency bandindices by using equation (1) and transmits the at least one PDCCHs bymeans of the corresponding frequency band transmitter (506).

In short, the PDCCH transmission procedure according to the fourthembodiment of the present invention is performed as follows. When noPDCCH is required to be transmitted in the current frequency band, thePDCCH transmission procedure is terminated. When at least one PDCCH isrequired to be transmitted in the current frequency band, the PDCCH istransmitted on the CCEs of which indices are interpreted into thefrequency band indices by using equation (1).

The base station apparatus is configured as shown in FIG. 9 and canoperate as shown in one of FIGS. 10 to 13 to transmit multiple PDCCHs.The user equipment must be configured to receive the multiple PDCCHs forallocating resources in different frequency bands through one of thefrequency bands and process the multiple PDCCHs received in thefrequency band.

FIG. 14 is a block diagram illustrating a configuration of a userequipment for receiving multiple PDCCHs in different frequency bandaccording to an exemplary embodiment of the present invention.

As shown in FIG. 14, the user equipment includes an f1 receiver 610, anf2 receiver 620, an f3 receiver 630, an f4 receiver 640, a frequencyband selector 650, and a resource selector 660. The user equipment isprovided with multiple frequency band receivers that are responsible forreceiving signals in the corresponding frequency bands. In FIG. 14, fourfrequency band receivers 610 to 640 operating on the frequency bands f1to f4 are depicted as an example, each of the f1 to f4 receivers 610 to640 includes an RF receiver 612 for receiving radio frequency signaltransmitted by the base station through corresponding frequency band,down-converting the radio frequency signal into base band signal, andconverting the base band analog signal into digital signal; a CP remover613 for removing the CP from the signal output by the RF receiver 612;an FFT 614 for performing FFT on the signal output by the CP remover 613to recover the signal that are IFFT converted by the base station; aplurality of PDCCH receivers 611-1 to 611-N for extracting the PDCCHsfrom the signal output by the FFT 614; and a PDSCH receiver 616 forextracting the PDSCH from the signal output by the FFT 714. Thefrequency band selector 650 selects one of PDCCHs output by the multiplePDCCH receiver 611-1 to 611-N, and the resource selector 660 providesthe f1 to f4 receivers 610 to 640 with the information on the PDCCHselected by the frequency band selector 650 to locate the resourcesallocated in the corresponding frequency bands.

As described above, each frequency band receiver of the user equipmentconverts the RF signal transmitted by the base station into a basebandsignal and then a digital signal by means of the RF receiver 612,removes a CP from the digital by means of the CP remover 613, andperforms FFT conversion by means of the FFT 614 so as to outputfrequency domain signals in parallel. The frequency domain signals areoutput to the corresponding PDCCH receivers 611-1 to 611-N and the PDSCHreceiver 616. The PDCCH receiver 611-1 to 611-N outputs the PDCCHsextracted from the frequency domain signals to the frequency bandselector 650, and the frequency band selector 650 output the PDCCHs tothe resource selector 660 selectively such that the resource selector660 provides the frequency band receivers 610, 620, 630, and 640 withthe information on the resources allocated in the respective frequencybands. Accordingly, the frequency band receivers 610, 620, 630, and 640can decode the PDSCHs of the respective frequency bands on the basis ofthe resource location information provided by the resource selector 660.

FIG. 15 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the first embodiment ofthe present invention.

Referring to FIG. 15, when a control channel is received in a frequencyband, the user equipment first determines whether a number of PDCCHsreceived in the current frequency band is equal to or less than one(702). If the number of PDCCHs received in the current frequency band isequal to or less than one, then the user equipment determines whetherthe number of PDCCHs received in the current frequency band is one(704). If the number of PDCCHs received in the current frequency band isnot one (i.e. if no PDCCH is received), then the user equipmentterminates the PDCCH processing procedure. Otherwise, if the number ofPDCCHs received in the current frequency band is one, then the userequipment locates the resource indicated by the PDCCH in the currentfrequency band and demodulates the data transmitted using the resource(706) and terminates the PDCCH processing procedure. If the number ofthe PDCCHs received in the current frequency band is not equal to orless than one (i.e. if multiple PDCCHs are received in the currentfrequency band) at step 702, then the user equipment demodulates themultiple PDCCHs and arranges the PDCCHs in ascending order of indices ofthe CCEs on which the PDCCHs are transmitted (708). Next, the userequipment interprets the CCE indices into the indices of frequency bandsexcluding the frequency band in which one PDCCH is transmitted (710).Finally, the user equipment locates the resources indicated by thePDCCHs in the frequency bands identified using the frequency bandindices obtained by interpreting the CCE indices and demodulates thedata transmitted using the resources located in respective frequencyband (712), and terminates the PDCCH processing procedure.

In the data reception method according to the first embodiment of thepresent invention, the user equipment terminates the PDCCHs processingprocedure immediately when no PDCCH is received in the current frequencyband; demodulates, when one PDCCH is received in the current frequencyband, the data transmitted in the resource indicated by the PDCCH withinthe current frequency band; and demodulates, when multiple PDCCHs arereceived in the current frequency band, the data transmitted in theresources indicated by the PDCCHs in the frequency bands identifiedusing the frequency band indices obtained by interpreting the indices ofthe CCEs on which the PDCCHs are transmitted.

FIG. 16 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the second embodiment ofthe present invention.

Referring to FIG. 16, when a physical control channel is received in afrequency band, the user equipment first determines whether a number ofPDCCHs received in the current frequency band is equal to or less thanone (802). If the number of PDCCHs received in the current frequencyband is equal to or less than one, then the user equipment determineswhether the number of PDCCHs received in the current frequency band isone (804). If the number of PDCCHs received in the current frequencyband is not one (i.e. if no PDCCH is received), the user equipmentterminates the PDCCH processing procedure. Otherwise, if the number ofPDCCHs received in the current band is one, then the user equipmentlocates the resource indicated by the PDCCH in the current frequencyband and demodulates the data transmitted using the resource (806) andterminates the PDCCH processing procedure. If the number of PDCCHsreceived in the current frequency band is not equal to or less than one(i.e. if multiple PDCCHs are received in the current frequency band) atstep 802, then the user equipment demodulates the multiple PDCCHs (808).Next, the UE checks the indices of the CCEs on which the PDCCHs aretransmitted and interprets the first indices of the sets of CCEscarrying the respective PDCCHs (including the PDCCHs for allocating theresource of a frequency band in which one PDCCH is transmitted already)into the frequency band indices by using equation (1) (810). Next, theuser equipment locates the resources indicated by the PDCCHs in therespective frequency bands identified using the frequency band indicesobtained by interpreting the CCE indices and demodulates the datatransmitted using the resources located in the respective frequency band(812), and terminates the PDCCH processing procedure. It is noted thatthe frequency bands in which one PDCCH is transmitted are included ascandidate frequency bands for locating resources at step 810. That is,the user equipment searches entire frequency bands, including those inwhich one PDCCH is transmitted, for the resources allocated.

In the data reception method according to the second embodiment of thepresent invention, the user equipment terminates the PDCCH processingprocedure immediately when no PDCCH is received in the current frequencyband; demodulates, when on e PDCCH is received in the current frequencyband, the data transmitted in the resource indicated by the PDCCH withinthe current frequency band; and demodulates, when multiple PDCCHs arereceived in the current frequency band, the data transmitted in theresources indicated by the PDCCHs in the frequency bands identifiedusing the frequency band indices obtained by interpreting the CCEindices by using the equation (1).

FIG. 17 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the third embodiment ofthe present invention.

Referring to FIG. 17, when a physical control channel is received in afrequency band, the user equipment first determines whether a number ofPDCCHs received in the current frequency band is equal to or less thanone (902). If the number of PDCCHs received in the current frequencyband is equal to or less than one, then the user equipment determineswhether the number of PDCCHs received in the current frequency band isone (904). If the number of PDCCHs received in the current frequencyband is not one (i.e. if n PDCCH is received), the user equipmentterminates the PDCCH processing procedure. Otherwise, if the number ofPDCCHs received in the current band is one, then the user equipmentlocates the resource indicated by the PDCCH in the current frequencyband and demodulates the data transmitted using the resource (906) andterminates the PDCCH processing procedure. If the number of PDCCHsreceived in the current frequency band is not equal to or less than on(i.e. if multiple PDCCHs are received in the current frequency band) atstep 902, then the user equipment demodulates the multiple PDCCHs (908).Next, the UE checks the indices of the CCEs on which the PDCCHs aretransmitted and interprets the first indices of the sets of CCEscarrying the respective PDCCHs (excluding the PDCCHs for allocating theresource of a frequency band in which on PDCCH is transmitted already)into the frequency band indices by using equation (1). Next, the userequipment locates the resources indicated by the PDCCHs in therespective frequency bands identified using the frequency band indicesobtained by interpreting the CCE indices using equation (1) anddemodulates the data transmitted using the resources located in therespective frequency band on the basis of the PDCCHs (912), andterminates the PDCCH processing procedure. It is noted that thefrequency bands in which one PDCCH is transmitted are excluded ascandidate frequency bands for locating resources at step 910. That is,the user equipment searches the frequency bands, excluding those inwhich one PDCCH is transmitted, for the resources allocated.

In the data reception method according to the third embodiment of thepresent invention, the user equipment terminates the PDCCH processingprocedure immediately when no PDCCH is received in the current frequencyband; demodulates, when one PDCCH is received in the current frequencyband, the data transmitted in the resource indicated by the PDCCH withinthe current frequency band; and demodulates, when multiple PDCCHs arereceived in the current frequency band, the data transmitted in theresources indicated by the PDCCHs in the frequency bands identifiedusing the frequency band indices obtained by interpreting the CCEindices by using the equation (1).

FIG. 18 is a flowchart illustrating a data reception method for anOFDMA-based communication system according to the fourth embodiment ofthe present invention.

Referring to FIG. 18, when a physical control channel is received in afrequency band, the user equipment first determines whether at least onePDCCH is received in the current frequency band (1002). If no PDCCH isreceived, the user equipment terminates the PDCCH processing procedureimmediately. Otherwise, if at least one PDCCH is received in the currentfrequency band, then the user equipment checks the CCE indicesreferencing the at least one PDCCHs and interprets the CCE indices intothe frequency band indices by using equation (1) (1004). Next, the userequipment demodulates the data transmitted using the resources locatedin the at least one frequency band on the basis of the PDCCHs (1006) andterminates the PDCCH processing procedure.

In the data processing method according to the fourth embodiment of thepresent invention, the user equipment first checks the number of PDCCHsreceived in the current frequency band, acquires, when at least onePDCCH is received in the current frequency band, the frequency bandindices by interpreting the indices of the CCEs on which the PDCCHs aretransmitted using equation (1), and demodulates the data transmittedusing the resources located with reference to the PDCCHs.

As described above, the resource allocation method for OFDMA-basedcommunication system according to an exemplary embodiment of the presentinvention is advantageous to allocate resources of different frequencybands by transmitting multiple PDCCHs through a control channel of oneof the frequency bands without increasing control information overhead.In an OFDMA-based communication system according to an exemplaryembodiment of the present invention, the base station transmits themultiple PDCCHs having implicit CCE indices through a control channel ofone of the frequency bands, and the user equipment interpret the CCEindices into frequency band indices and locates the resources allocatedin the different frequency bands using the PDCCHs of the frequency bandsindicated by the frequency band indices.

While certain embodiments of the present invention have been illustratedand described, it will be clear that the present invention and itsadvantages are not limited to these embodiments only. Numerousmodifications, changes, variations, substitutions and equivalents willbe apparent to those skilled in the art without departing from thespirit and scope of the present invention as described in the claims.

What is claimed:
 1. A Physical Downlink Control Channel (PDCCH)transmission method of a base station for a mobile communication systembased on an Orthogonal Frequency Division Multiple Access (OFDMA),comprising: acquiring downlink control information of a resourcecorresponding to a carrier among a plurality of carriers; identifying atleast one Control Channel Element (CCE) index based on an indicator ofthe carrier among the plurality of carriers; generating a PDCCH for thedownlink control information based on the identified CCE index; andtransmitting the PDCCH through a predetermined carrier.